Abstract's details
Assessment of internal wave propagation through combined observations from SWOT (sea surface height and backscatter coefficient) and Sentinel-1 (surface roughness and Doppler radial velocities)
Event: 2025 SWOT Science Team Meeting
Session: Oceanography: Tides and Inertia-Gravity Waves
Presentation type: Poster
Until recently, the study of internal waves (IWs) in the ocean has primarily relied on high-resolution imagery, such as Synthetic Aperture Radar (SAR) and optical sensors. However, prior to the launch of the Surface Water and Ocean Topography (SWOT) mission, detecting the sea surface height (SSH) perturbations associated with these waves was challenging due to the limited spatial resolution of conventional nadir altimeters. As a swath-based SAR interferometer, the Ka-band Radar Interferometer (KaRIn) onboard SWOT provides not only SSH measurements but also the backscatter signal (sigma0), which can be directly compared to sigma0 or surface roughness products derived from Sentinel-1 SAR data.
In this study, we present a novel analysis conducted in the coastal region offshore of the Congo River mouth, based on the synergistic use of SWOT (250 m) and Sentinel-1 (10 m) observations. On both sides of the submarine canyon associated with the Congo River (north and south), internal waves are clearly detected in both the SSH and sigma0 products from KaRIn. On October 24th, 2023, Sentinel-1 sampled the region approximately 2.5 hours after the SWOT overpass. By tracking the internal wave fronts in both SWOT sigma0 and Sentinel-1 roughness maps, we estimated the phase velocity of the waves.
Two distinct phase velocities were identified: a slower propagation (~0.3 m/s) north of the canyon and a faster one (~0.8 m/s) to the south. These differences likely result from variations in environmental conditions, including stratification, bathymetry, and background currents. For instance, Doppler-derived radial velocities from Sentinel-1 reveal opposing ocean currents of up to 0.5 m/s in the northern region, which counteract internal wave propagation. In contrast, southern currents are weaker and aligned with the direction of wave propagation, likely facilitating faster wave speeds.
Moreover, in the case of internal waves, simultaneous knowledge of the phase velocity and sea surface height (SSH) along the direction of propagation is particularly valuable, as these parameters are linearly related to the orbital surface velocities (Gill, 1982). Analyzing the spatial gradients of SSH along the wave crest allows the identification of convergence and divergence zones at the surface, potentially related to vertical velocities of the waves. These dynamic features correspond to modulations in surface roughness and are reflected in the variations of the backscatter signal (sigma0) observed by SWOT. These waves are also detected in the 2km SWOT SLA data.
Gill, A. E. (1982). Atmosphere—ocean dynamics. Academic Press.
Back to the list of abstractIn this study, we present a novel analysis conducted in the coastal region offshore of the Congo River mouth, based on the synergistic use of SWOT (250 m) and Sentinel-1 (10 m) observations. On both sides of the submarine canyon associated with the Congo River (north and south), internal waves are clearly detected in both the SSH and sigma0 products from KaRIn. On October 24th, 2023, Sentinel-1 sampled the region approximately 2.5 hours after the SWOT overpass. By tracking the internal wave fronts in both SWOT sigma0 and Sentinel-1 roughness maps, we estimated the phase velocity of the waves.
Two distinct phase velocities were identified: a slower propagation (~0.3 m/s) north of the canyon and a faster one (~0.8 m/s) to the south. These differences likely result from variations in environmental conditions, including stratification, bathymetry, and background currents. For instance, Doppler-derived radial velocities from Sentinel-1 reveal opposing ocean currents of up to 0.5 m/s in the northern region, which counteract internal wave propagation. In contrast, southern currents are weaker and aligned with the direction of wave propagation, likely facilitating faster wave speeds.
Moreover, in the case of internal waves, simultaneous knowledge of the phase velocity and sea surface height (SSH) along the direction of propagation is particularly valuable, as these parameters are linearly related to the orbital surface velocities (Gill, 1982). Analyzing the spatial gradients of SSH along the wave crest allows the identification of convergence and divergence zones at the surface, potentially related to vertical velocities of the waves. These dynamic features correspond to modulations in surface roughness and are reflected in the variations of the backscatter signal (sigma0) observed by SWOT. These waves are also detected in the 2km SWOT SLA data.
Gill, A. E. (1982). Atmosphere—ocean dynamics. Academic Press.